深入浅出JavaScript前端中的设计模式

class Singleton {
    let _instance = null;
    static getInstance() {
        if (!Singleton._instance) {
          Singleton.instance = new Singleton()
        }
        // 如果这个唯一的实例已经存在，则直接返回
        return Singleton._instance
    }
}
const s1 = Singleton.getInstance()
const s2 = Singleton.getInstance()

class Restaurant{
    constructor(){
        this.menuData = {};
    }
    // 获取菜品
    getDish(dish){
        if(!this.menuData[menu]){
            console.log("菜品不存在，获取失败");
            return;
        }
        return this.menuData[menu];
    },
    // 添加菜品
    addMenu(menu,description){
        if(this.menuData[menu]){
            console.log("菜品已存在，请勿重复添加");
            return;
        }
        this.menuData[menu] = menu;
    }
    // 移除菜品
    removeMenu(menu){
        if(!this.menuData[menu]){
            console.log("菜品不存在，移除失败");
            return;
        }
        delete this.menuData[menu];
    },
}
class Dish{
    constructor(name,description){
        this.name = name;
        this.description = description;
    }
    eat(){
        console.log(`I'm eating ${this.name},it's ${`this.description);
    }
}

interface bookDataType1 {
  book_id: number;
  status: number;
  create: string;
  update: string;
}
interface bookDataType2 {
  id: number;
  status: number;
  createTime: number;
  updateAt: string;
}
interface bookDataType3 {
  book_id: number;
  status: number;
  createTime: number;
  updateAt: number;
}
const getTimeStamp = function (str: string): number {
  //.....转化成时间戳
  return timeStamp;
};
//适配器
export const bookDataAdapter = {
  adapterType1(list: bookDataType1[]) {
    const bookDataList: bookData[] = list.map((item) => {
      return {
        book_id: item.book_id,
        status: item.status,
        createAt: getTimeStamp(item.create),
        updateAt: getTimeStamp(item.update),
      };
    });
    return bookDataList;
  },
  adapterType2(list: bookDataType2[]) {
    const bookDataList: bookData[] = list.map((item) => {
      return {
        book_id: item.id,
        status: item.status,
        createAt: item.createTime,
        updateAt: getTimeStamp(item.updateAt),
      };
    });
    return bookDataList;
  },
  adapterType3(list: bookDataType3[]) {
    const bookDataList: bookData[] = list.map((item) => {
      return {
        book_id: item.book_id,
        status: item.status,
        createAt: item.createTime,
        updateAt: item.updateAt,
      };
    });
    return bookDataList;
  },
};

if ( 'food' == '苹果') {
      水煮()
} else if ('food' == '胡萝卜') {
      炒了()
} else if ('food' == '鱼') {
      清蒸()
} else if ('food' == '猪肉') {
      炸了()
} else if ('food' == '牛肉') {
      烤了()
} else {
      生吃()
}
// 用了策略模式，看起来舒服多了
let wayObj = {
    '苹果': 水煮(),
    '胡萝卜': 炒了(),
    '鱼': 清蒸(),
    '猪肉': 炸了(),
    '牛肉': 烤了(),
    '不知道': 生吃()
}

// 观察者模式 被观察者Subject 观察者Observer Subject变化 notify观察者
let observerIds = 0;
// 被观察者Subject
class Subject {
  constructor() {
    this.observers = [];
  }
  // 添加观察者
  addObserver(observer) {
    this.observers.push(observer);
  }
  // 移除观察者
  removeObserver(observer) {
    this.observers = this.observers.filter((obs) => {
      return obs.id !== observer.id;
    });
  }
  // 通知notify观察者
  notify() {
    this.observers.forEach((observer) => observer.update(this));
  }
}
// 观察者Observer
class Observer {
  constructor() {
    this.id = observerIds++;
  }
  update(subject) {
    // 更新
  }
}

class Event {
  constructor() {
    this.eventEmitter = {};
  }
  // 订阅
  on(type, fn) {
    if (!this.eventEmitter[type]) {
      this.eventEmitter[type] = [];
    }
    this.eventEmitter[type].push(fn);
  }
  // 取消订阅
  off(type, fn) {
    if (!this.eventEmitter[type]) {
      return;
    }
    this.eventEmitter[type] = this.eventEmitter[type].filter((event) => {
      return event !== fn;
    });
  }
  // 发布
  emit(type) {
    if (!this.eventEmitter[type]) {
      return;
    }
    this.eventEmitter[type].forEach((event) => {
      event();
    });
  }
}